Growing cultures of several strains of Pseudomonas fluorescens and Pseudomonas chlororaphis produced N2O as the only detectable gaseous product of denitrification, and other strains produced N2 as the gaseous end product of denitrification. All of the nitrogen in NO3- or NO2- added to cell suspensions of the N2O-producing strains P. fluorescens PJ 185 and P. chlororaphis B-560 was recovered as N2O. All of the nitrogen in NO3- or NO2- added to cell suspensions of the N2-producing strain P. fluorescens PJ70 was converted to N2. Cell extracts of P. fluorescens PJ 70, PJ 185, and P. chlororaphis B-560 exhibited NO3- reductase activity when sodium succinate was the electron donor. Reduced nicotinamide adenine dinucleotide and flavine adenine dinucleotide were required to demonstrate NO2- reductase activity in cell extracts.
Resting cells of Corynebacterium nephridii reduce nitrate, nitrite, and nitric oxide to nitrous oxide under anaerobic conditions. Nitrous oxide production from nitrite was optimal from pH 7.0 to 7.4. The stoichiometry of nitrous oxide production from nitrite was 99% of the theoretical-two moles of nitrite was used for each mole of nitrous oxide detected. Hydroxylamine increases gas evolution from nitrite but inhibits the reduction of nitric oxide to nitrous oxide. Hydroxylamine is converted to nitrogenous gas(es) by resting cells only in the presence of nitrite. Under certain conditions nitric oxide, as well as nitrous oxide, was detected.
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